For meeting the increasing demand for more bandwidth, higher data rate, less latency and greater data security, chips having higher operating frequencies (e.g. in microwaves and millimeter wave frequency ranges) are used for developing wireless systems. But the higher the frequency, the higher the attenuation of the transmission path. For overcoming this attenuation, the wireless systems need antennas with high efficiency and gain. Antennas are the essential elements of wireless systems.
In wireless systems, antennas are integrated either in the chip, on the interposer or on the printed circuit board (system board). Chip-integrated antennas can result in higher system miniaturization and cost reduction since the same can be manufactured together with the chip at the same time. Above that, the electric connection between a front-end chip and an antenna is very short. However, such antennas have very little efficiency and gain which is due to the higher permittivity of chip material (e.g. silicon) as well as the substrate and metallization losses of the chip technologies. Thus, the same are not suitable for developing future high-frequency systems. Antennas that are integrated either on the interposer or on the printed circuit board can have much higher efficiency and gain as long as the antennas are manufactured with high-frequency substrates.
However, the signal path between a front-end chip and an antenna integrated on an interposer or a printed circuit board is long and consists of many geometric discontinuities (e.g. chip connections such as wire bonds, lines with bends, vias, etc.). This path causes signal integrity problems such as reflection, attenuation, signal delay, crosstalk and also undesired radiation, which decrease the entire system performance.
For preventing these problems, the antennas have to be integrated very close to the front-end chip. For that, system integration platforms allowing such integration are indispensable.
In conventional technology, there are several approaches how system integration has been established. Fan-out wafer level package (FO-WLP)-based system integration platforms have the potential of ensuring such integration. In FOWLP, no interposers are used, the integration of antennas can take place on the same substrate in which the chips are embedded. Thereby, the signal path between chips and antenna is reduced and the signal integrity problems are alleviated.
The three leading examples of FO-WLP-based system integration platforms are:                Embedded Wafer Level Ball Grid Array (eWLB) by Infineon [1]        Redistributed Chip Package (RCP) by Freescale [2]        Integrated Fan-Out WLP (InFO-WLP) by TSMC [3]        
So far, eWLB and InFO-WLP have been used and demonstrated for wireless systems. FIGS. 5a and 5b represent eWLB and InFO-WLP with integrated antennas.
FIG. 5a shows a combination of PCB 32 with eWLB 36 including a chip (e.g. RF chip) 38 as well as an antenna 42 arranged in the redistribution layer 40 of the eWLB 36. For improving the signal radiation characteristic, a reflector 44 is provided opposite to the antenna 42 on the PCB board 32.
FIG. 5b shows InFO-WLB integration. Here, the chip 38 is embedded in a cast resin 39, wherein the redistribution layer 40 is provided on the bottom side of the chip. Antenna elements 42 are arranged on the opposite side of the redistribution layer 40.
In eWLB, the radiating element of the antenna is integrated on the redistribution layer (RDL) and the reflector is integrated on the printed circuit board. Thereby, the functionality of the antennas and also of the platform depends on the dimensions of the package contacting, e.g. BGA balls and their process variations as well as on the printed circuit board technology. Thereby, the FOWLP system integration platform can be optimized only in connection with the contacts/BGA balls, the printed circuit board technologies and the underfill materials.
The antennas in eWLB and in InFO cannot be optimized without adapting the dimensions of the RDL and the mold material, which limits the freedom of design of the platform.
Both in eWLB and in InFO, the fields of the integrated antennas are not shielded from the chips and other integrated components. The undesired interaction can result in EMC problems.
In eWLB, the radiation of an integrated antenna cannot cover the entire hemisphere (the entire horizontal and vertical layer) without causing undesired coupling with other integrated components. The reason for that is that other components are integrated on the same layer as the antennas. Thus, there is a need for an improved approach.